JP7431417B2 - Hexagonal boron nitride powder, resin composition, resin sheet, and method for producing hexagonal boron nitride powder - Google Patents

Description

The present invention relates to hexagonal boron nitride powder, a resin composition, a resin sheet, and a method for producing hexagonal boron nitride powder.

In electronic components, hexagonal boron nitride is used as a material with dielectric strength and thermal conductivity. As a method for producing a single crystal of hexagonal boron nitride, for example, the flux method disclosed in Patent Document 1 is known. Further, as methods for producing hexagonal boron nitride powder, for example, the melamine method disclosed in Patent Documents 2 and 3, the gas phase method disclosed in Patent Document 4, etc. are known as conventional techniques.

Japanese Patent Application Publication No. 2016-141600 Japanese Patent Application Publication No. 10-059702 JP2006-188411A International Publication No. 2015/122378

However, in the conventional techniques as described above, there is room for improvement from the viewpoint of realizing a resin sheet exhibiting high thermal conductivity and high dielectric strength. One aspect of the present invention is to provide hexagonal boron nitride powder that can realize a resin sheet with high thermal conductivity and high dielectric strength.

In order to solve the above problems, the present inventor conducted intensive research and found that by using a powder containing agglomerated particles in which hexagonal boron nitride primary particles of a specific shape were aggregated, high thermal conductivity and high dielectric strength were achieved. We have discovered that it is possible to produce a resin sheet with That is, the present invention includes the following configuration.

The hexagonal boron nitride primary particles contain aggregated hexagonal boron nitride particles, have a specific surface area of 0.5 m ² /g or more and 5.0 m ² /g or less, and have a major axis of 0. A hexagonal boron nitride powder having a size of .6 μm or more and 4.0 μm or less, and an aspect ratio of 1.5 or more and 5.0 or less.

It includes a heating step of heating a mixed powder containing boron oxide, an organic compound containing nitrogen, and lithium carbonate, and the weight ratio of boron atoms to nitrogen atoms in the mixed powder is 0.2 or more and 0.4 or less. The weight ratio of boron atoms to lithium carbonate in the mixed powder is 0.22 or more and 0.98 or less, and in the heating step, the mixed powder is heated at a maximum temperature of 1200°C or more and 1500°C or less. A method for producing hexagonal boron nitride powder.

According to one aspect of the present invention, it is possible to provide hexagonal boron nitride powder that can realize a resin sheet with high thermal conductivity and high dielectric strength.

It is a figure which shows the scanning electron microscope image of the hexagonal boron nitride powder based on Example 1, (a) is a figure enlarged 2000 times, (b) 5000 times, and (c) is a figure enlarged 10000 times. . It is a figure which shows the scanning electron microscope image of the hexagonal boron nitride powder based on Example 2, (a) is a figure enlarged 2000 times, (b) 5000 times, and (c) is a figure enlarged 10000 times. . It is a figure which shows the scanning electron microscope image of the hexagonal boron nitride powder based on the comparative example 7, (a) is a figure enlarged 2000 times, (b) 5000 times, and (c) is a figure enlarged 10000 times. . It is a figure which shows the scanning electron microscope image of the hexagonal boron nitride powder based on the comparative example 8, (a) is a figure enlarged 2000 times, (b) 5000 times, and (c) is a figure enlarged 10000 times. . 1 is a graph of particle size distribution of hexagonal boron nitride powders according to Examples 1 and 2 and Comparative Examples 7 and 8.

An embodiment of the present invention will be described below, but the present invention is not limited thereto.

<1. Hexagonal boron nitride powder>
The hexagonal boron nitride powder according to an embodiment of the present invention includes hexagonal boron nitride aggregate particles in which hexagonal boron nitride primary particles aggregate, and has a specific surface area of 0.5 m ² /g or more and 5.0 m ² /g. and the major axis of the hexagonal boron nitride primary particles is 0.6 μm or more and 4.0 μm or less, and the aspect ratio is 1.5 or more and 5.0 or less.

The hexagonal boron nitride powder includes hexagonal boron nitride agglomerated particles formed by agglomeration of plate-shaped hexagonal boron nitride primary particles having a small particle size and a thick wall at a high density. Therefore, a resin sheet made using hexagonal boron nitride powder has improved anisotropy and is densely packed with hexagonal boron nitride powder, thereby exhibiting high thermal conductivity and high dielectric strength.

Furthermore, since the hexagonal boron nitride powder has a small content of fine powder, it is possible to effectively suppress an increase in viscosity when kneading it into a resin. As a result, since the hexagonal boron nitride powder has excellent filling properties into resin, a resin sheet made using the hexagonal boron nitride powder further exhibits high thermal conductivity and high dielectric strength.

In this specification, hexagonal boron nitride primary particles mean a single particle of hexagonal boron nitride. Hereinafter, the hexagonal boron nitride primary particles will also be referred to as h-BN primary particles. The h-BN primary particles are usually plate-like particles. In this specification, the maximum diameter on the plate surface of this plate-like particle is referred to as the major axis. Further, the length perpendicular to the plate surface is called the thickness. The value obtained by dividing this major axis by the thickness is called the aspect ratio.

The major axis of h-BN primary particles is preferably 0.6 μm or more and 4.0 μm or less, more preferably 1.0 μm or more and 3.5 μm or less, and 1.5 μm or more and 3.5 μm or less. It is even more preferable that there be. The aspect ratio of the h-BN primary particles is preferably 1.5 or more and 5.0 or less, more preferably 2.0 or more and 4.5 or less, and 2.5 or more and 4.0 or less. It is more preferable that The fact that the major axis and aspect ratio of the h-BN primary particles are within the above ranges indicates that the h-BN primary particles are small-diameter, thick-walled plate-like particles. Furthermore, when the major axis and aspect ratio of the h-BN primary particles are within the above ranges, the obtained aggregated particles are approximately spherical, so gaps are less likely to be formed in the aggregated particles, and an increase in the viscosity of the resin composition can be suppressed. Note that in this specification, the major axis and aspect ratio of h-BN primary particles represent average values measured by the measuring method described in Examples below.

In this specification, hexagonal boron nitride aggregated particles mean particles in which h-BN primary particles are aggregated. The long axis of the hexagonal boron nitride agglomerated particles is usually 5 to 40 μm. Hereinafter, hexagonal boron nitride aggregate particles are also referred to as h-BN aggregate particles. The shape of the h-BN agglomerated particles has the shape shown in FIGS. 1 and 2, for example, a substantially spherical shape formed by at least two or more h-BN primary particles connected in the thickness direction, and the substantially spherical particle. It has a shape in which h-BN primary particles are connected in a beaded shape, or a shape in which large and small h-BN primary particles are agglomerated facing in multiple directions.

The hexagonal boron nitride powder comprises h-BN agglomerated particles. In the following, hexagonal boron nitride powder is also referred to as h-BN powder. The h-BN powder may further include h-BN primary particles. That is, the h-BN powder may be a mixture of h-BN primary particles and h-BN agglomerated particles.

The specific surface area of the h-BN powder is preferably 0.5 m ² /g or more and 5.0 m ² /g or less, more preferably 1.0 m ² /g or more and 4.5 m ² /g or less. It is preferably 1.5 m ² /g or more and more preferably 4.0 m ² /g or less. When the h-BN primary particles are relatively thick, the specific surface area of the h-BN powder tends to fall within the above range. Further, the fact that the specific surface area of the h-BN powder is 0.5 m ² /g or more means that relatively small h-BN primary particles in the h-BN powder are appropriately agglomerated. As a result, the resin sheet produced using the h-BN powder according to an embodiment of the present invention has improved anisotropy and good thermal conductivity.

Furthermore, the fact that the specific surface area of the h-BN powder is 5.0 m ² /g or less means that the content of fine powder contained in the h-BN powder is small and the content of thick h-BN primary particles is large. . If the fine powder content is small, an increase in the viscosity of the resin composition is suppressed when the h-BN powder is kneaded into the resin. Therefore, it is easy to fill the h-BN powder into the resin. As a result, the resin sheet produced using the h-BN powder according to one embodiment of the present invention exhibits good thermal conductivity and good dielectric strength.

The tap bulk density of the h-BN powder according to an embodiment of the present invention is preferably 0.40 g/cm ³ or more, more preferably 0.45 g/cm ³ or more, and 0.50 g/cm 3 or more. More preferably, it is ³ or more. A tap bulk density of 0.40 g/ ^cm3 or more means that h-BN primary particles having a specific shape are moderately agglomerated to form h-BN powder with a highly filling particle size distribution. represents. That is, if the tap bulk density is 0.40 g/cm ³ or more, the h-BN aggregated particles are not coarse and/or the h-BN aggregate particles have good filling properties into the resin composition. As a result, the resin sheet produced using the h-BN powder according to one embodiment of the present invention is less likely to have voids and exhibits uniform thermal conductivity. Note that a particle size distribution with high packing property means that h-BN primary particles and h-BN aggregate particles having various particle diameters are appropriately contained. For example, when h-BN powder contains only h-BN primary particles or h-BN aggregated particles having a single particle size, voids are likely to occur between the h-BN primary particles or h-BN aggregated particles. , it is difficult to pack densely.

D95 of the h-BN powder according to one embodiment of the present invention is preferably 5 to 15 μm, more preferably 5 to 12 μm, and even more preferably 5 to 10 μm. Note that D95 represents a particle diameter at which the cumulative volume frequency in the particle size distribution curve is 95%. If D95 is 15 μm or less, the h-BN powder according to one embodiment of the present invention does not contain particles with a large particle size, and therefore, even when a thin resin sheet is formed using the h-BN powder, Also, smoothness of the resin sheet surface can be obtained. In other words, by using the h-BN powder according to an embodiment of the present invention, it becomes easier to produce a thin resin sheet. Furthermore, if the D95 of the h-BN powder is 5 μm or more, it is greater than the average particle diameter of the h-BN primary particles, which means that the h-BN primary particles are not monodispersed and are sufficiently aggregated. Recognize.

Further, D10 of the h-BN powder according to an embodiment of the present invention is preferably 1.5 μm or more, more preferably 1.8 μm or more, and even more preferably 2.0 μm or more. . Note that D10 represents a particle diameter at which the cumulative volume frequency in the particle size distribution curve is 10%. It can be seen that when D10 is 1.5 μm or more, the amount of fine powder contained in the h-BN powder is small.

The viscosity of the resin when filled with h-BN powder (resin filling viscosity) is preferably lower. For example, 20% by volume of h-BN powder is added to silicone resin (CY52-276A manufactured by Dow Toray Industries, Inc.). The resin filling viscosity when filled is preferably 130 Pa·S or less, more preferably 125 Pa·S or less. By setting the resin filling viscosity to 130 Pa·S or less, the h-BN powder can be filled into the resin with high density. Furthermore, since the resin has good fluidity, the resin sheet can be easily produced.

The h-BN powder has a DBP absorption amount (mL/100g) calculated from the curve of the horizontal axis: DBP dripping amount (mL) and the vertical axis: torque (Nm), which was measured in accordance with JIS-K-6217-4. ), it is preferably 70 mL/100 g or less, more preferably 65 mL/100 g or less, and even more preferably 60 mL/100 g or less. By having a DBP absorption amount of 70 mL/100 g or less, an increase in resin filling viscosity can be suppressed compared to h-BN powder having the same specific surface area and a DBP absorption amount of more than 70 mL/100 g.

<2. Resin composition>
A resin composition according to one embodiment of the present invention includes the above-described h-BN powder and resin. The method for producing the resin composition is not particularly limited, and the resin composition can be produced by a known production method.

(2-1. Resin)
The resin is not particularly limited, and may be, for example, a silicone resin or an epoxy resin. Examples of the epoxy resin include bisphenol A type epoxy resin, bisphenol S type epoxy resin, bisphenol F type epoxy resin, bisphenol A type hydrogenated epoxy resin, polypropylene glycol type epoxy resin, polytetramethylene glycol type epoxy resin, and naphthalene type epoxy resin. Examples include epoxy resin, phenylmethane type epoxy resin, tetrakisphenolmethane type epoxy resin, biphenyl type epoxy resin, epoxy resin having a triazine nucleus in its skeleton, and bisphenol A alkylene oxide adduct type epoxy resin. These epoxy resins may be used alone or in combination of two or more. Furthermore, amine resins, acid anhydride resins, phenol resins, imidazoles, etc. may be used as the curing agent. These curing agents may be used alone or in combination of two or more. The amount of these curing agents to be blended with the epoxy resin is 0.5 to 1.5 equivalent ratio, preferably 0.7 to 1.3 equivalent ratio with respect to the epoxy resin. In this specification, these curing agents are also included in the resin.

Furthermore, as the silicone resin, any known curable silicone resin which is a mixture of an addition reaction type silicone resin and a silicone crosslinking agent can be used without any limitation. Examples of the addition reaction type silicone resin include polyorganosiloxanes such as polydimethylsiloxane having an alkenyl group such as a vinyl group or hexenyl group as a functional group in the molecule. Examples of silicone-based crosslinking agents include dimethylsiloxane-methylhydrogensiloxane copolymer endblocked with dimethylhydrogensiloxy groups, dimethylsiloxane-methylhydrogensiloxane copolymer endblocked with trimethylsiloxy groups, and poly(trimethylsiloxane endblocked). Examples include polyorganosiloxanes having silicon-bonded hydrogen atoms such as methylhydrogensiloxane) and poly(hydrogensilsesquioxane). Further, as the curing catalyst, any known platinum-based catalyst used for curing silicone resins can be used without limitation. Examples include fine particulate platinum, fine particulate platinum supported on carbon powder, chloroplatinic acid, alcohol-modified chloroplatinic acid, olefin complexes of chloroplatinic acid, palladium, and rhodium catalysts.

The blending ratio of the resin and h-BN powder in the resin composition according to an embodiment of the present invention may be determined as appropriate depending on the application. can be blended in an amount of 30 to 90% by volume, more preferably 40 to 80% by volume, even more preferably 50 to 70% by volume.

(2-2. Other ingredients)
The resin composition may contain components other than hexagonal boron nitride and the resin. Such components are referred to herein as "other components."

For example, in the resin composition, part of the h-BN powder may be replaced with an inorganic filler. Examples of the inorganic filler include aluminum oxide, silicon oxide, zinc oxide, magnesium oxide, titanium oxide, silicon nitride, aluminum nitride, aluminum hydroxide, magnesium hydroxide, silicon carbide, calcium carbonate, barium sulfate, and talc.

Furthermore, the resin composition may contain curing accelerators, discoloration inhibitors, surfactants, dispersants, coupling agents, colorants, plasticizers, viscosity modifiers, antibacterial agents, etc. within a range that does not affect the effects of the present invention. may be included as appropriate.

Applications of the resin composition according to an embodiment of the present invention include, for example, adhesive films, sheet-like laminate materials (resin sheets) such as prepregs, circuit boards (laminated board applications, multilayer printed wiring board applications), solder resists, and underlayers. - Fill materials, thermal adhesives, die bonding materials, semiconductor sealing materials, hole-filling resins, component embedding resins, thermal interface materials (sheets, gels, grease, etc.), power module substrates, heat dissipation materials for electronic components, etc. Can be done.

<3. Resin sheet＞
A resin sheet according to one embodiment of the present invention includes the above-mentioned resin composition. The resin sheet can also be said to be a sheet formed from a resin composition. The thickness of the resin sheet can be appropriately set depending on the application, and may be, for example, 20 to 200 μm, 20 to 100 μm, or 20 to 50 μm. Generally, thin resin sheets have excellent thermal conductivity, but tend to have poor dielectric strength. Since the resin sheet according to one embodiment of the present invention contains the above-mentioned h-BN powder, it can have both excellent thermal conductivity and dielectric strength even when it is relatively thin. The method of forming the resin composition into a sheet shape is not particularly limited, and any known method can be used.

It is preferable that the resin sheet has a plane orientation index B of 0.95 or less. Planar orientation index B is calculated from the following formula.
Planar orientation index B=log(A/6.67)
In the formula, A represents the peak ratio between the (002) plane and the (100) plane derived from h-BN primary particles as determined by XRD measurement, and is calculated from the following formula. In addition, in the following formula, the value of the peak derived from the (002) plane is simply expressed as (002), and the value of the peak derived from the (100) plane is simply expressed as (100).
Peak ratio A=(002)/(100)
When the plane orientation index B of the resin sheet is 0.95 or less, the produced resin sheet has improved anisotropy and exhibits good thermal conductivity. The closer the plane orientation index B is to 0, the more the highly thermally conductive planes of the h-BN primary particles are oriented in a state close to perpendicular to the plane direction of the resin sheet. In this specification, "anisotropy" means, for example, that the resin sheet has good thermal conductivity in the plane direction, but poor thermal conductivity in the thickness direction. Furthermore, "improved anisotropy" indicates that the thermal conductivity in the thickness direction of the resin sheet has been improved.

The resin sheet preferably has a thermal conductivity of 3.5 W/m・K or more, and preferably 4.5 W/m・K or more, as measured in accordance with the temperature wave thermal analysis method (ISO22007-3). is more preferable. If the thermal conductivity is 3.5 W/m·K or more, the resin sheet has good thermal conductivity.

Withstand voltage can be used as an index of dielectric strength of a resin sheet. The resin sheet preferably has a withstand voltage of 30 kV/mm or more, preferably 35 kV/mm or more, as measured in accordance with "5.8 Withstand voltage (molding materials)" of JIS K6911:2006 General Test Methods for Thermosetting Plastics. More preferably, it is equal to or larger than mm. If the withstand voltage is 30 kV/mm or more, the resin sheet has good insulation properties.

Further, if the thermal conductivity is 3.5 W/m·K or more and the withstand voltage is 30 kV/mm or more, the resin sheet has both high thermal conductivity and high dielectric strength.

<4. Manufacturing method of hexagonal boron nitride powder>
A method for producing h-BN powder according to an embodiment of the present invention includes a heating step of heating a mixed powder containing boron oxide, an organic compound containing nitrogen, and lithium carbonate. By this manufacturing method, it is possible to obtain h-BN powder used for manufacturing the resin sheet that exhibits the above-mentioned high thermal conductivity and high dielectric strength.

(4-1. Mixed powder)
Examples of the boron oxide contained in the mixed powder include diboron trioxide (boron oxide), diboron dioxide, tetraboron trioxide, tetraboron pentoxide, borax, and anhydrous borax, among which diboron trioxide It is preferable to use The use of diboron trioxide as the boron oxide is industrially advantageous because inexpensive raw materials are used. Note that two or more types of boron oxides may be used in combination.

Examples of the nitrogen-containing organic compound contained in the mixed powder include melamine, ammeline, ammelide, melam, melon, dicyandiamide, and urea, among which it is preferable to use melamine. The use of melamine as the nitrogen-containing organic compound is industrially advantageous because inexpensive raw materials are used. Note that two or more types of nitrogen-containing organic compounds may be used in combination.

When melted, lithium carbonate becomes a flux that acts as an auxiliary agent for growing h-BN primary particles. Furthermore, when lithium carbonate is used, there is a tendency to easily obtain h-BN primary particles having a specific shape as described above.

The mixed powder may contain an alkali carbonate such as calcium carbonate or sodium carbonate in addition to boron oxide, a nitrogen-containing organic compound, and lithium carbonate.

The weight ratio (B/N) of boron atoms to nitrogen atoms in the mixed powder is preferably 0.2 or more and 0.4 or less, more preferably 0.25 or more and 0.35 or less. When the B/N is 0.2 or more, a B source can be secured and a sufficient yield can be secured. Further, by setting the B/N to 0.4 or less, a sufficient N source for nitriding can be secured. Note that the nitrogen atoms in the mixed powder heated in the heating step are derived from an organic compound containing nitrogen, and the boron atoms in the mixed powder heated in the superheating step are derived from boron oxide.

The weight ratio of boron atoms to lithium carbonate (B/Li ₂ CO ₃ ) in the mixed powder is preferably 0.22 or more and 0.98 or less, more preferably 0.30 or more and 0.80 or less. preferable. When B/Li ₂ CO ₃ is 0.22 or more, the amount of flux can be appropriately suppressed, so that h-BN primary particles can be appropriately aggregated. Further, since a sufficient amount of flux can be formed by setting B/Li ₂ CO ₃ to 0.98 or less, h-BN primary particles having a specific shape can be uniformly obtained.

(4-2. Heating process)
In the heating step, the mixed powder is preferably heated at a maximum temperature of 1200°C or more and 1500°C or less. By heating the mixed powder at a temperature of 1200° C. or higher, it is possible to prevent the particle diameter of the h-BN primary particles from becoming excessively small and to suppress the aspect ratio from becoming large. The maximum temperature is more preferably 1250°C or higher, and even more preferably 1300°C or higher. Furthermore, by heating the mixed powder at a temperature of 1500° C. or lower, it is possible to prevent the volatilization of lithium carbonate, and it is also possible to suppress an increase in the particle size and aspect ratio of the h-BN primary particles. More preferably, the maximum temperature is 1450°C or less.

In the heating step, the mixed powder is preferably heated under an inert gas atmosphere under normal pressure or reduced pressure. By heating in the above environment, damage to the heating furnace body can be suppressed. In this specification, the term "under an inert gas atmosphere" refers to a state in which an inert gas is introduced into a container in which the mixed powder is heated, and the gas inside the container is replaced with the inert gas. The inert gas inflow rate is not particularly limited, but the inert gas inflow rate is 5 L/min. It may be more than that. Further, the inert gas may be, for example, nitrogen gas, carbon dioxide gas, or argon gas.

In the heating step, a preferable method is to place the mixed powder inside a reaction container in which gas exchange does not occur during the heating step. In the heating step, the boron oxide contained in the mixed powder is used in the h-BN powder production reaction, but some of it is volatilized by heating and is therefore not used in the h-BN powder production reaction. Here, by arranging the mixed powder inside a reaction container where gas exchange does not occur during the heating step, volatilization of boron oxide from the mixed powder can be suppressed. Thereby, the amount of boron oxide used in the h-BN powder production reaction can be increased, and the yield of h-BN powder can be improved.

In this specification, "no gas exchange occurs" means that the gas inside the reaction container and the gas outside the reaction container are not exchanged. In the heating step, gas is generated inside the reaction vessel due to the progress of the h-BN powder production reaction and the volatilization or decomposition of the mixed powder. Therefore, it is not necessary to intentionally introduce gas from the outside into the reaction container, and there is no need to completely prevent the gas inside the reaction container from being released to the outside of the reaction container.

The structure, size, shape, material, etc. of the reaction vessel are not particularly limited, and should have sufficient durability, heat resistance, pressure resistance, corrosion resistance, etc., taking into consideration manufacturing conditions such as heating temperature and raw materials. can be determined.

As a mechanism for preventing gas exchange from occurring, for example, a reaction vessel with a lid may be used as the reaction vessel. If the reaction container has a lid, the lid separates it from the outside, so it is possible to suppress the inflow of gas from outside the reaction container, and gas exchange does not occur.

In addition, if the reaction container is completely sealed, the inside of the container may be affected by the progress of the h-BN powder production reaction, the generation of gas due to volatilization or decomposition of the mixed powder, or the expansion of gas inside the reaction container due to heating. pressure increases. In such a case, there is a risk that the reaction vessel may be damaged, or there may be restrictions on the material and shape of the reaction vessel in order to make the reaction vessel a pressure-resistant structure. Therefore, it is preferable to appropriately release the excess gas inside the reaction vessel within a range that does not significantly affect the yield of h-BN powder.

Examples of methods for releasing excess gas inside the reaction container include a method of attaching a pressure regulating valve to the reaction container, a method of making a small hole in the reaction container, and the like. In addition, if the reaction container is a container with a lid, by placing the lid on the top of the reaction container and placing it on top without fixing it, the reaction container will be sealed by its own weight when the internal pressure is low. When the internal pressure increases, the lid is lifted and the gas inside the reaction vessel is discharged to the outside. Therefore, by using a container with a lid, it is possible to easily prevent gas exchange while releasing excess gas inside the reaction container, which is cited as a preferred form. In this case, the weight of the lid per unit area is preferably in the range of 5 kg/m ² to 20 kg/m ² . Note that the weight of the lid per unit area is the value obtained by dividing the weight of the lid by the area of the lid facing the internal space of the reaction container.

The shape of the reaction container is not particularly limited, and any shape such as cylindrical or rectangular can be used. The shape of the reaction vessel is preferably cylindrical from the perspective of preventing damage to the reaction vessel due to repeated heating and cooling, and from the perspective of effectively utilizing space and improving production efficiency when installed in a heating furnace. A rectangular shape is preferred.

The material of the reaction vessel is not particularly limited as long as it can withstand the heating temperature of 1200° C. or higher and 1500° C. or lower, which is the heating temperature in the heating step, and may be mainly composed of alumina, titania, zirconia, silica, magnesia and calcia, or silica and alumina. Examples include various ceramic sintered bodies such as cordierite and mullite. In addition, from the viewpoint of preventing contamination of h-BN powder, which is a reaction product, it is also a preferable embodiment to use boron nitride as the material of the reaction vessel. A preferable embodiment is to coat the surface (and the surface with which the produced h-BN powder comes into contact) with boron nitride.

The amount of mixed powder placed inside the reaction vessel is not particularly limited, but if it is too small, the vapor phase inside the reaction vessel will be large, and the volatilization of boron oxide will not be sufficiently suppressed, limiting the yield improvement effect. It becomes a target. On the other hand, if the amount of the mixed powder is too large, the pressure inside the reaction vessel tends to increase because there is little gas phase. Therefore, the volume occupied by the mixed powder in the reaction vessel is preferably within the range of 50% to 90%, more preferably 60% to 80%, of the volume of the reaction vessel. Note that in this specification, the volume occupied by the mixed powder is the volume of the portion occupied by the mixed powder including voids between particles of the mixed powder when placed in a reaction container.

The method of heating the mixed powder placed inside a reaction container where gas exchange does not occur is not particularly limited, but it is preferable to place the reaction container in a heating furnace and heat it to a desired temperature because it can be easily carried out. It is a form.

(4-3. Other processes)
The method for producing h-BN powder may include steps other than the heating step. Such steps are referred to herein as "other steps." Other steps included in the method for producing h-BN powder include, for example, a mixing step, an acid washing step, a water washing step, a drying step, and a classification step.

The mixing step is a step of mixing boron oxide, an organic compound containing nitrogen, lithium carbonate, etc. before the heating step. By mixing the mixed powder in advance, the reaction proceeds substantially uniformly, so that fluctuations in the particle diameter, etc. of the produced h-BN primary particles are suppressed.

The acid washing step is a step in which lithium carbonate, boron oxide, or a composite oxide of lithium carbonate and boron oxide, etc. attached to the h-BN powder are removed by washing the h-BN powder with acid. In the acid washing step, it is preferable to use a dilute acid such as hydrochloric acid. The acid cleaning method is not particularly limited, and may be acid cleaning by showering, acid cleaning by soaking, or acid cleaning by stirring.

The water washing step is a step of washing the h-BN powder with water in order to remove the acid attached to the h-BN powder during the acid washing step. The water washing method is not particularly limited, and after filtering the h-BN powder, water washing may be performed by showering, or water washing may be performed by soaking.

The drying step is a step of drying the prepared h-BN powder. The drying method is not particularly limited, such as high temperature drying or reduced pressure drying.

The classification step is a step in which h-BN powder is divided according to particle size and/or particle shape. The classification operation may be sieving, wet classification or air classification.

The present invention is not limited to the embodiments described above, and various modifications can be made within the scope of the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. are also included within the technical scope of the present invention.

〔summary〕
[1] Contains hexagonal boron nitride agglomerated particles in which hexagonal boron nitride primary particles are aggregated, and has a specific surface area of 0.5 m ² /g or more and 5.0 m ² /g or less, and the hexagonal boron nitride primary particles A hexagonal boron nitride powder having a major axis of 0.6 μm or more and 4.0 μm or less and an aspect ratio of 1.5 or more and 5.0 or less.

[2] The hexagonal boron nitride powder according to [1], which has a tapped bulk density of 0.40 g/cm ³ or more.

[3] The hexagonal boron nitride powder according to [1] or [2], which has a D95 of 5 to 15 μm as measured by particle size distribution measurement.

[4] A resin composition comprising the hexagonal boron nitride powder according to any one of [1] to [3] and a resin.

[5] A peak ratio of the (002) plane and the (100) plane derived from the hexagonal boron nitride primary particles, A=(002)/(100), which includes the resin composition according to [4], and is determined by XRD measurement. A resin sheet having a plane orientation index B=log(A/6.67) calculated from 0.95 or less.

[6] A heating step of heating a mixed powder containing a boron oxide, an organic compound containing nitrogen, and lithium carbonate, wherein the weight ratio of boron atoms to nitrogen atoms in the mixed powder is 0.2 or more, 0. The weight ratio of boron atoms to lithium carbonate in the mixed powder is 0.22 or more and 0.98 or less, and in the heating step, the mixed powder is heated at a maximum temperature of 1200°C or more and 1500°C. A method for producing hexagonal boron nitride powder, which is heated as follows.

[7] The method for producing hexagonal boron nitride powder according to [6], wherein the heating step is performed by placing the mixed powder inside a reaction container in which gas exchange does not occur during the heating step.

An embodiment of the present invention will be described below.

[Evaluation method of h-BN primary particles]
<Long diameter/aspect ratio>
The major axis and aspect ratio of h-BN primary particles were measured using FE-SEM (manufactured by Hitachi High-Technologies, Ltd.: S5500). 100 different h-BN primary particles were randomly selected from images observed with a scanning electron microscope at a magnification of 5,000 times, and the length and thickness of the major axis of the h-BN primary particles were measured, and the aspect ratio (length of major axis/ (thickness length) was calculated, and the average value was taken as the aspect ratio. Further, the length of the major axis was determined by calculating the average value of the measured values.

[Evaluation method of h-BN powder]
<Specific surface area>
The specific surface area of the h-BN powder was measured using Macsorb HM model-1201 manufactured by Mountech.

<Thermal conductivity>
The thermal conductivity (W/m·K) of the resin sheet was determined by thermal diffusivity (m ² /sec)×density (kg/m ³ )×specific heat (J/kg·K).

Thermal diffusivity was measured using the temperature wave thermal analysis method (ai-Phase Mobile u, ISO22007-3), the density was measured using the Archimedes method (XS204V manufactured by Mettler Toledo), and the specific heat was measured using the differential scanning calorimeter (DSC) method. (Rigaku Corporation: Thermo Plus Evo DSC8230).

<Withstand voltage>
The withstand voltage (kV/mm) of the resin sheet was determined using a withstand voltage tester YPAD-0225 manufactured by Keinan Electric Co., Ltd., and 5.8 Withstand voltage (molding Materials).

<Planar orientation index>
The plane orientation index of the resin sheet was measured using XRD. As a measuring device, a fully automatic horizontal multipurpose X-ray diffraction device SmartLab manufactured by Rigaku was used. The measurement conditions were a scan speed of 20 degrees/min, a step width of 0.02 degrees, and a scan range of 10 to 90 degrees.

<Particle size distribution>
The particle size distribution of the h-BN powder was measured using a particle size distribution measuring device MT3000 manufactured by Nikkiso Co., Ltd. Note that the measurement sample was prepared by the method shown below. First, 20 g of ethanol was added as a dispersion medium to a 50 mL screw tube bottle, and 1 g of h-BN powder was dispersed in the ethanol. Next, using an ultrasonic homogenizer (SONIFIER SFX250) manufactured by BRANSON, the tip was placed 10 mm from the bottom of the screw tube, and ultrasonication was performed at an amplitude of 40% for 20 minutes. Then, the particle size distribution of the measurement sample subjected to the ultrasonic treatment was measured.

<Tap bulk density>
The tap bulk density of the h-BN powder was measured using Tap Denser KYT-5000 manufactured by Seishin Enterprise Co., Ltd. A 100 mL sample cell was used, and the measurement conditions were a tap speed of 120 times/min, a tap height of 5 cm, and a tap count of 500 times.

<Resin filling viscosity>
A resin composition prepared by filling silicone resin (CY52-276A manufactured by Dow Toray Industries, Inc.) with 20% by volume of h-BN powder was measured using a rheometer (TA Instruments AR2000ex) at a temperature of 25°C and a shear rate of 1. /S viscosity was measured. This viscosity was defined as the resin filling viscosity.

<DBP absorption amount>
DBP absorption amount (mL/100g) calculated from the curve of h-BN powder measured in accordance with JIS-K-6217-4, horizontal axis: DBP dripping amount (mL), vertical axis: torque (Nm) I asked for As the measuring device, S-500 manufactured by Asahi Souken Co., Ltd. was used. The measurement conditions were a DBP dropping rate of 4 mL/min, a stirring blade rotation speed of 125 rpm, a sample input amount of 15 to 25 g, and a dropping amount of 70% of the maximum torque to determine the DBP absorption amount. As DBP (Dibutyl Phthalate), Wako Pure Chemical Industries, Ltd.: special grade reagent (seller code 021-06936) was used.

[Example 1]
First, a mixed powder was prepared by mixing 14.6 g of boron oxide as a boron oxide, 24 g of melamine as an organic compound containing nitrogen, and 10.4 g of lithium carbonate. In the produced mixed powder, B/N was 0.28, and B/Li ₂ CO ₃ was 0.44.

In the heating step, the prepared mixed powder was heated in a nitrogen atmosphere at a maximum temperature of 1400° C. for 1 hour to produce h-BN powder. The prepared h-BN powder was acid-washed with a 5% aqueous hydrochloric acid solution, filtered, washed with water, and dried. FIG. 1 is a diagram showing scanning electron microscope images of the h-BN powder according to Example 1, in which (a) is 2,000 times magnified, (b) is 5,000 times, and (c) is photographed with 10,000 times magnification. It is a diagram.

As a base resin, a mixture of 100 parts by weight of an epoxy resin (JER806 manufactured by Mitsubishi Chemical Corporation) and 28 parts by weight of a curing agent (alicyclic polyamine curing agent, JER Cure 113 manufactured by Mitsubishi Chemical Corporation) was prepared.

Next, 40% by volume of each base resin and 60% by volume of the prepared h-BN powder were mixed using methyl ethyl ketone as a solvent, and then the solvent was dried to obtain a resin composition.

The dried resin composition was cast into a mold body, and cured using a heat press at a temperature of 150°C, a pressure of 5 MPa, and a holding time of 1 hour, resulting in a diameter of 10 mm and a thickness of 0.15 mm. A sheet was prepared.

[Example 2]
h-BN powder, a resin composition, and a resin sheet were produced in the same manner as in Example 1 except that the maximum temperature in the heating step was 1500°C. FIG. 2 is a diagram showing scanning electron microscope images of the h-BN powder according to Example 2, in which (a) is 2000 times magnified, (b) is 5000 times, and (c) is photographed at 10000 times magnification. It is a diagram.

[Example 3]
In the heating step, the prepared mixed powder was placed in a reaction vessel with a lid on top to prevent gas exchange. The reaction container with a lid has an inner dimension of 170 mm x 170 mm x height of 30 mm (volume 867000 mm ³ ), and the weight of the lid is 300 g (weight of lid per unit area: 0.0104 g/mm ² ). Then, h-BN powder was produced in the same manner as in Example 1, except that the reaction vessel with a lid containing the mixed powder was placed in a batch firing furnace and heated. The volume of the mixed powder in the reaction container with a lid was 578000 mm ³ , and the volume occupied by the mixed powder in the reaction container with a lid was 67%.

[Comparative example 1]
As Comparative Example 1, a mixed powder was prepared by mixing 14.6 g of boron oxide as a boron oxide, 40 g of melamine as an organic compound containing nitrogen, and 10.4 g of lithium carbonate. The produced mixed powder had a B/N of 0.17 and a B/Li ₂ CO ₃ of 0.44. h-BN powder, a resin composition, and a resin sheet were produced in the same manner as in Example 2 except that the amount of melamine was increased.

[Comparative example 2]
As Comparative Example 2, a mixed powder was prepared by mixing 14.6 g of boron oxide as a boron oxide, 12.3 g of melamine as an organic compound containing nitrogen, and 10.4 g of lithium carbonate. The produced mixed powder had a B/N of 0.55 and a B/Li ₂ CO ₃ of 0.44. h-BN powder, a resin composition, and a resin sheet were produced in the same manner as in Example 2 except that the amount of melamine was small.

[Comparative example 3]
As Comparative Example 3, a mixed powder was prepared by mixing 14.6 g of boron oxide as a boron oxide, 24 g of melamine as an organic compound containing nitrogen, and 3.76 g of lithium carbonate. The produced mixed powder had a B/N of 0.28 and a B/Li ₂ CO ₃ of 1.22. h-BN powder, a resin composition, and a resin sheet were produced in the same manner as in Example 2 except that the amount of lithium carbonate was small.

[Comparative example 4]
As Comparative Example 4, a mixed powder was prepared by mixing 14.6 g of boron oxide as a boron oxide, 24 g of melamine as an organic compound containing nitrogen, and 25 g of lithium carbonate. The produced mixed powder had a B/N of 0.28 and a B/Li ₂ CO ₃ of 0.18. h-BN powder, a resin composition, and a resin sheet were produced in the same manner as in Example 2 except that the amount of lithium carbonate was increased.

[Comparative example 5]
As Comparative Example 5, h-BN powder, a resin composition, and a resin sheet were produced in the same manner as in Example 1 except that the maximum temperature in the heating step was changed to 1100°C.

[Comparative example 6]
As Comparative Example 6, h-BN powder, a resin composition, and a resin sheet were produced in the same manner as in Example 1 except that the maximum temperature in the heating step was changed to 1600°C.

[Comparative example 7]
A resin composition and a resin sheet were produced in the same manner as in Example 1, except that the h-BN powder was changed to AP-10S manufactured by MARUKA Corporation. FIG. 3 is a diagram showing scanning electron microscope images of h-BN powder according to Comparative Example 7, in which (a) is 2000 times magnified, (b) is 5000 times, and (c) is photographed at 10000 times magnification. It is a diagram.

[Comparative example 8]
A resin composition and a resin sheet were produced in the same manner as in Example 1, except that the h-BN powder was changed to RBN manufactured by Nissin Refratec Co., Ltd. FIG. 4 is a diagram showing scanning electron microscope images of hexagonal boron nitride powder according to Comparative Example 8, in which (a) is taken at a magnification of 2,000 times, (b) is a magnification of 5,000 times, and (c) is taken at a magnification of 10,000 times. This is a diagram.

〔result〕
Tables 1 to 3 show the manufacturing conditions and physical properties of h-BN powder and resin sheets. Furthermore, Table 4 shows the yield of h-BN powder. The yield was calculated as the amount of h-BN powder actually obtained relative to the amount of h-BN produced calculated from the amount of boron atoms in the raw material mixed powder.

実施例１～３では、長径およびアスペクト比が特定の範囲であるｈ－ＢＮ一次粒子、並びに比表面積が特定の範囲であるｈ－ＢＮ粉末が得られた。また、実施例１および実施例２にて作製したｈ－ＢＮ粉末はいずれも樹脂充填粘度が低いため、樹脂に対してｈ－ＢＮ粉末を高密度に充填できると考えられる。さらに、樹脂シートの面配向指数も０．９５以下を示し、異方性が改善されていた。そして、実施例１および実施例２にて作製した樹脂シートは、熱伝導性および絶縁耐力ともに良好であった。以上のことより、長径およびアスペクト比が特定の範囲であるｈ－ＢＮ一次粒子を凝集させたｈ－ＢＮ凝集粒子を含み、かつ比表面積が特定の範囲であるｈ－ＢＮ粉末を用いることにより、高熱伝導性および高絶縁耐力を示す樹脂シートが得られることがわかる。

In Examples 1 to 3, h-BN primary particles having major diameters and aspect ratios within a specific range, and h-BN powders having a specific surface area within a specific range were obtained. Furthermore, since both the h-BN powders produced in Example 1 and Example 2 have low resin filling viscosity, it is thought that the resin can be filled with h-BN powder at high density. Furthermore, the plane orientation index of the resin sheet was 0.95 or less, indicating that the anisotropy was improved. The resin sheets produced in Example 1 and Example 2 had good thermal conductivity and dielectric strength. From the above, by using h-BN powder that contains h-BN aggregated particles that are agglomerated h-BN primary particles whose major axis and aspect ratio are in a specific range, and whose specific surface area is in a specific range, It can be seen that a resin sheet exhibiting high thermal conductivity and high dielectric strength can be obtained.

Moreover, when comparing Example 1 and Example 3, Example 3, in which the mixed powder was placed inside a reaction vessel in which gas exchange does not occur in the heating process, uses a reaction vessel in which gas exchange does not occur. It was possible to produce h-BN with a higher yield than in Example 1, which did not contain the same.

In the production method of Comparative Example 1, which had a lower B/N than Example 2, the major axis of the h-BN primary particles became longer. Furthermore, h-BN powder is considered to have poor filling properties due to its low tap bulk density. The resin sheet obtained using this h-BN powder also had a plane orientation index of over 0.95 and was anisotropic. This resin sheet also had poor thermal conductivity.

In the production method of Comparative Example 2 in which the B/N was higher than in Example 2, the aspect ratio of the h-BN primary particles was increased. Furthermore, since the h-BN powder has a high resin packing density, it is considered that the filling property is poor. The resin sheet obtained using this h-BN powder also had a plane orientation index of over 0.95 and was anisotropic. This resin sheet also had poor dielectric strength.

In the production method of Comparative Example 3 in which B/Li ₂ CO ₃ was higher than in Example 2, the aspect ratio of h-BN primary particles was increased. Furthermore, since the h-BN powder has a large specific surface area and resin packing density, it is considered to have poor filling properties. The resin sheet obtained using this h-BN powder also had a plane orientation index of over 0.95 and was anisotropic. This resin sheet also had poor dielectric strength.

In the production method of Comparative Example 4 in which B/Li ₂ CO ₃ was lower than in Example 2, the major axis of the h-BN primary particles became longer. Furthermore, h-BN powder is considered to have poor filling properties due to its low tap bulk density. The resin sheet obtained using this h-BN powder also had a plane orientation index of over 0.95 and was anisotropic. This resin sheet also had poor thermal conductivity.

In the production method of Comparative Example 5 in which the maximum temperature in the heating step was lower than that in Example 2, the major axis of the h-BN primary particles became smaller and the aspect ratio became larger. Furthermore, h-BN powder is considered to have poor filling properties because it has a large specific surface area, D95, and resin packing density. The resin sheet obtained using this h-BN powder also had a plane orientation index of over 0.95 and was anisotropic. This resin sheet also had poor thermal conductivity.

In the production method of Comparative Example 6, in which the maximum temperature in the heating step was higher than in Example 2, the major axis and aspect ratio of the h-BN primary particles were increased. Furthermore, h-BN powder has a small tap bulk density and a large D95, so it is considered to have poor filling properties. The resin sheet obtained using this h-BN powder also had a plane orientation index of over 0.95 and was anisotropic. This resin sheet also had poor thermal conductivity.

In Comparative Example 7, AP-10S manufactured by MARUKA Corporation, which has a large aspect ratio and a large specific surface area, is considered to have poor filling properties because of its high resin filling viscosity. The resin sheet using this h-BN powder also had a plane orientation index exceeding 0.95 and was anisotropic. This resin sheet was inferior in thermal conductivity and dielectric strength.

In Comparative Example 8, RBN manufactured by Nissin Refura Co., Ltd., which has a large specific surface area and a small tap bulk density, has a high resin filling viscosity and is therefore considered to have poor filling properties. The resin sheet using this h-BN powder also had a plane orientation index exceeding 0.95 and was anisotropic. This resin sheet also had poor thermal conductivity.

INDUSTRIAL APPLICATION This invention can be utilized for an electronic component excellent in thermal conductivity and dielectric strength.

Claims (7)

Contains hexagonal boron nitride aggregate particles in which hexagonal boron nitride primary particles aggregate,
The specific surface area is 0.5 m ² /g or more and 5.0 m ² /g or less,
A hexagonal boron nitride powder, wherein the hexagonal boron nitride primary particles have a major axis of 0.6 μm or more and 4.0 μm or less, and an aspect ratio of 1.5 or more and 4.0 or less. The hexagonal boron nitride powder according to claim 1, having a tap bulk density of 0.40 g/cm ³ or more. The hexagonal boron nitride powder according to claim 1 or 2, which has a D95 of 5 to 15 μm as measured by particle size distribution measurement. A resin composition comprising the hexagonal boron nitride powder according to any one of claims 1 to 3 and a resin. comprising the resin composition according to claim 4,
Planar orientation index B = log (A/6. 67) is 0.95 or less. A heating step of obtaining hexagonal boron nitride powder by heating a mixed powder containing boron oxide, an organic compound containing nitrogen, and lithium carbonate,
The weight ratio of boron atoms to nitrogen atoms in the mixed powder is 0.2 or more and 0.4 or less,
The weight ratio of boron atoms to lithium carbonate in the mixed powder is 0.22 or more and 0.98 or less,
In the heating step, the mixed powder is heated at a maximum temperature of 1200°C or more and 1500°C or less. 7. The method for producing hexagonal boron nitride powder according to claim 6, wherein the heating step is performed by placing the mixed powder inside a reaction container in which gas exchange does not occur during the heating step.

Images